The present invention relates to latex film compounds having enhanced tear resistance, tensile strength, and aging properties without any sacrifices in elasticity (elongation).
Although latex products are well known in the art, an inherent problem associated with these products is the degradation of these products over time due to oxidation which shortens the useful life of the latex product. In the case of natural rubbers, oxidation results in chain scission which in turns causes a gooey, sticky rubber whereas in the case of synthetic rubbers, oxidation results in further cross-linking of the carbon chains which in turn causes a stiff and brittle rubber. It follows that producing a latex product which is more resistant to oxidation would produce a product with enhanced tear resistance, tensile strength, elasticity and a longer useful life.
Latex products are commonly produced by curing a mixture of a polymer or copolymer, a stabilizing system and a curing system comprised of an accelerator an activator and a crosslinker.
In order to make the latex product more resistant to oxidation, an antioxidant is also added during production of the latex compound. Mercaptoarylazole compounds have previously been used as antioxidants. However, mercaptoarylazole compounds can also serve as accelerators. U.S. Pat. No. 4,435,532 used 2-mercaptobenzothiazole (col. 4, Example 4) as a heat stabilizer and deemed that xe2x80x9cThis class of compounds is unusable due to its powerfully accelerating effect on vulcanization since it restricts the possibility of processing the product and does not provide the necessary reliability in operation.xe2x80x9d
Surprisingly, the applicant has discovered that combining an anti-oxidant with a mercaptoarylazole compound results in latex products which possess enhanced tear resistance, tensile strength, elongation and a longer useful life.
It is an object of the invention to enhance the tear resistance, tensile strength, elasticity and aging properties of a latex product by adding an antioxidant and an antioxidant synergist to a latex compound comprising a polymer, a stabilizing system, a film surface conditioner and a curing system comprised of an accelerator, an activator and a crosslinker.
The basic components of the latex product of the current invention comprise a polymer, a stabilizing system, a film surface conditioner and a curing system comprising an accelerator, an activator and a crosslinker. To this composition, an antioxidant and an antioxidant synergist was added.
The polymer can be selected from any number of polymers and copolymers associated with the making of latex products and can be selected from the group consisting of natural rubber, acrylonitrile, polychloroprene, styrene butadiene, butyl, isoprene, ethylene propylene diene, chlorosulfonated polyethylene, and carboxylated and hydrogenated derivatives thereof.
The stabilizing system can be selected from any number of stabilizers commonly associated with the making of latex products and can be selected from the group consisting of modifiers of pH like ammonia, sodium and potassium hydroxide, tetrasodium pyrophosphate, amines, caseinate, glues, gelatin, natural and synthetic gums, organic soaps and surfactants.
The curing system is comprised of an activator, a crosslinker and an accelerator.
Suitable accelerators for the curing system can be selected from the group consisting of thiazoles, sulfenamides, dithiocarbamates, thiurams, xanthates, thioureas, guanidines, aldehyde amines and peroxides.
Suitable activators for the curing system can be selected from the group consisting of metal oxides such as zinc oxide, magnesium oxide and lead oxide.
Suitable cross-linkers for the curing system can be selected from the group consisting of sulfur, zinc oxide, zinc chloride and carbon to carbon crosslinks initiated by peroxides.
The antioxidant can be selected from any number of antioxidants selected from the group consisting of amines, diamines, diphenylamines, octylated diphenylamines, reaction products of amines, phenols, alkylated phenols, arylated phenols, bisphenol A, isocyanurates, butyl phenols, fortified phenols, phosphited phenols, butylated phenols, phenolics, reaction products of p-cresol and cyclopentadiene, styrenated phenols, hydroquinolines and dithiocarbamates.
Preferred embodiments of the anti-oxidants are phenolic antioxidants or amine antioxidants.
The antioxidant synergist for the purposes of this invention is a mercaptoarylazole compound and salt forms thereof. This includes though is not limited to mercaptoarylthiazoles and mercaptoarylimidazole compounds. A preferred embodiment of the mercaptoarylthiazole is 2-mercaptobenzothiazole. Preferred embodiments of the mercaptoarylimidazole are 2-mercaptobenzimidazole (MBI) and 2-mercaptotoluimidazole (MTI). Preferred salt forms of the mercaptoarylazole compounds are zinc salts, e.g. zinc 2-mercaptobenzimidazole (ZMBI) and zinc 2-mercaptotoluimidazole (ZMTI).
It is noted that the term xe2x80x9cantioxidant synergistxe2x80x9d is distinguished from the term xe2x80x9cantioxidantxe2x80x9d in that the antioxidant synergist is able to enhance the antioxidative effect when added in combination with a primary antioxidant. However, using the antioxidant synergist alone may result in deterioration of one or more of the properties of the latex product, i.e. tensile strength, tear strength, elongation and/or useful life.
The sulfur, zinc oxide or peroxide cured rubber composition may also contain conventional additives including surfactants, reinforcing agents, fillers, peptizing agents, pigments, stearic acid, accelerators, sulfur vulcanizing agents, antiozonants, antioxidants, activators, initiators, plasticizers, waxes, prevulcanization inhibitors, fire retardants and colorants.
By adjusting the ratios of the antioxidants from 0.125 parts per hundred dry rubber (PHR) to 4 PHR and adjusting the antioxidant synergist from 0.1 PHR to 4 PHR, the tear strength of the latex film will improve from 5-100%.
For synthetic latex films, tear strength increased a minimum of 15-33% when an antioxidant and an antioxidant synergist were used.